The present invention relates generally to a medical cancer therapy facility and, more particularly, to a medical particle delivery system having a compact gantry design. Embodiments of the invention relate to apparatuses and methods for transfer scanning systems for use in cancer therapy.
Subject matter of the invention pertains to methods and apparatus for using, generating, controlling or detecting radiant energy, that is, energy propagated in the form of electromagnetic waves, or traveling subatomic, atomic or molecular particles, combinations and subcombinations including such methods or apparatus, and accessories therefore. In a medical setting, a cancerous object or other invasive material is irradiated by a stream of particles, generated in a medical synchrotron, for example, and delivered to a patient by way of a beam gantry. Medically-useful particles may include protons, neutrons, and atomic nuclei, such as those of tritium and carbon.
It has been known in the art to use a particle accelerator, such as a synchrotron, and a gantry arrangement to deliver a beam of particles, such as protons, from a single source to one of a plurality of patient treatment stations for cancer therapy. In such systems, the cancerous tumor will be hit and destroyed by particles in a precise way with a localized energy deposition.
Hadron cancer therapy facilities deliver particle beam energy localized in a patient's body. The beam energy is conformed to fit a targeted volume, such as a cancerous tumor. The beam energy is conformed to a tumor volume in three dimensions using two systems: A scanning system sweeps the beam to cover a tumor area, while a beam-energy control system modulates the energy level of the beam to determine dose depth, or longitudinal penetration, based on the Bragg-peak developed by the particle beam. Dose penetration is spanned using a range of beam energies, whereby the sharp Bragg peak characteristic of a mono-energetic beam can be widened, so that the depth of a tumor can be fathomed. The widened Bragg peak may be referred to as a spread-out Bragg peak (SOBP). Combined, transverse scanning and SOBP are employed to dose a tumor volume. In this way, radiation damage to healthy cells is dramatically reduced in comparison to other radiation treatments using photons (X and Gamma rays) or electrons, for example, which pass through the tumor to be treated, as well as through intervening and subsequent tissue.
Ion therapy is similar in concept to external beam radiation therapy—the idea is still to target and kill tumor cells by destroying their haywire DNA, but particle beams have properties that make them ideal for cancer therapy. The particle radiation therapy is done in 2 steps: 1) a three dimensional reconstruction of the tumor and its relationship to the surrounding structures and 2) a reproducible treatment position that minimizes movement errors. Initially, the scans are done by using tomography scans (CT) for region of interest and slices are determined in 2 to 3 millimeter intervals. The regions of interest are identified and marked for irradiating the tumors by a physician. Physicists and dosimetrist create a treatment plan by using a computer model that determines a series of angles and beams through the tumor. A medical doctor then reviews the plan. The treatment beams are also conformal beams shaped to the three-dimensional tumor.
Particle radiation treatment may be done by a scanning technique, such as single beam scanning and pencil beam scanning. Single beam scanning, also known in the art as uniform scanning, uses magnets to scan a broad beam across a treatment field. This type of scanning typically uses collimators to shape the beam. Collimators are large metal pieces that are carved out of beam-blocking or beam-absorbing metals, and directly shape the beam. Pencil or spot beam scanning is used to irradiate a tumor transversely, scanning across from the left to right and from top to bottom. The transverse beam spot scanning is done with the beam at a specific energy. A computer and device are programmed to carry out the method of transverse beam scanning by sweeping the beam in successive depth-layers of the tumor, reaching the extent of the tumor in the X-Y plane at each specific depth. The transverse scanning then moves to the next layer when the beam energy is changed, accordingly. Fast scanning magnets move the beam spot in X-Y direction, while quadrupole triplet magnets define the beam spot size at the patient.
Proton and carbon therapy facilities include an injector providing a beam from, starting from an ion source to an accelerator, and transport and delivery systems. The gantry delivery systems for proton and especially carbon ions typically are the most expensive part of any treatment facility. Delivery systems include a large bending magnet at the end as the scanners are placed before them. Apertures of the large bending magnets have to allow for beam motions on the order of +/−10 cm. Even in the case of proton therapy, which is a smaller device, the proton therapy device weighs with the magnets a minimum of 40 tons.
The gantry of a typical particle beam cancer therapy system accepts a particle beam of a required energy from the accelerator and projects it with high precision toward a cancerous tumor within a patient. Ions are accelerated by an accelerator and are shaped for delivery by a gantry. The ion particle energy is determined within the accelerator to allow their energy to be deposited in the tumor cells. The beam from an isocentric gantry must be angularly adjustable so that the beam can be directed into the patient under different angles of entrance. This flexibility is necessary to avoid radiation to the sensitive healthy organs or spine. Because of these requirements, the gantry of a conventional particle beam cancer therapy facility is typically the most expensive piece of equipment of the treatment facility and its magnets are generally very large and heavy.
For example, the proton-carbon medical therapy facility described by R. Fuchs and P. Emde in “The Heavy Ion Gantry of the HICAT Facility” includes an isocentric gantry system for delivery of protons, Helium, Carbon and Oxygen ions to patients. The gantry system has a total weight of 630 tons and the required beam line elements for transporting and delivering fully stripped Carbon and Oxygen ions with 430 MeV/nucleon kinetic energy have a total weight of 135 tons. The rotating part of the isocentric gantry system weighs about 570 tons due to its role to safely transport and precisely deliver ions to the patients. This extreme weight results in significant amount of structural cost for a building that can support this massive rotating gantry weight.
Further, another system, which is different than the present invention, is the Paul Scherrer Institute (PSI) proton therapy facility that contains a scanning method before entering into the dipole magnets. This technique performs the scanning prior to the bending of the particles. Specifically, the PSI proton facility bends protons in a large 40 tons dipole magnet. There is a need for a small gantry system that provides the same treatment options to a patient.
Further, a Source to Axis Distance (S.A.D.) defines the angle of arrival of a beam to a patient's skin. The optimal condition is a normal angle with beam spots which are parallel to each position, such that S.A.D.=∞. That is, the S.A.D. is preferred to be as large as possible. In a path toward gantry size reduction, a condition that creates a normal angle of incidence to the patients should not be abandoned.
U.S. Pat. No. 7,582,886, issued Sep. 1, 2009, U.S. Pat. No. 8,173,981, issued May 8, 2012, and U.S. Pat. No. 8,426,833, issued Apr. 23, 2013, all to Trbojevic, relate to medical particle therapy gantries, and are incorporated herein by reference in their entireties. U.S. Pat. No. 7,432,516 issued Oct. 7, 2008, to Peggs, et al., relates to rapidly cycling medical synchrotrons and beam delivery systems, and is incorporated herein by reference in its entirety.